1. Field of the Invention
Tricyclo[6.2.2.0.sup.3,8 ]dodecanes
2. Prior Art
The fragrance industry relies heavily on the use of natural oils and products derived from natural oils in the preparation of their fragrance materials. There has, of course, been a constant trend toward the use of synthetic materials since they offer many advantages over the naturally derived products.
Synthetics are usually less dependent upon the vagaries of naturally derived products such as availability, price, quality, crop failure etc. and there is normally better control over their quality and reproducibility. In addition, naturally derived products are often complex mixtures in which one or two chemicals provide the major odor impact. If a feasible route toward the synthesis of the more important odor contributors exists, such odorants can be used in their own right free of the by-products which are indigenous to the oil.
There has been success in synthesizing a number of naturally derived compounds and such synthetics are commercially availble in large quantities. As the natural products become more complex in structure, however, the problem of a commercially feasible synthesis becomes more difficult. Consequently, many synthetic routes developed for natural products are of academic interest only inasmuch as they require reagents which are not readily availble, sophisticated techniques which do not readily lend themselves to to large scale production and, often, complex separations.
One product used in the perfume industry is obtained by applying an acetylation procedure (e.g. acetic anhydride + polyphosphoric acid) to the hydrocarbon fractions of American cedarwood oil which consist essentially of 40-50% .alpha.-cedrene, 5-10% .beta.-cedrene and 40-50% cis thujopsene.
Kitchens et al. have shown that the most desirable odor components of the complex mixture obtained by acetylating American cedarwood oil are acetyl thujopsene derivatives [Garry C. Kitchens, Alan R. Hochstetler and Kent Kaiser, U.S. Pat. Nos. 3,678,119; 3,754,037; 3,681,470; 3,681,470; and Kitchens et al. J. Org. Chem. 37, 6 (1972) and J. Org. Chem. 37, 1 (1972)]. It was further disclosed in the above references that acetylation of pure (-)-thujopsene produced a product having a strong woody odor which upon analysis by gas chromatography revealed seven major components which were designated in order of elution as isomers A through G.
The major component, isomer G, constituted about half the mixture and possessed a powerful, woody, musk, ambergris odor far greater than that of any of the six other isomers. The structure of isomer G was shown to be 4-acetyl-1,7,7-trimethyltricyclo[6.2.2.0.sup.3,8 ]-3-dodecene, (1), (also known as 4-aceto-6,8a-ethano-1,1,6-trimethyl-1,2,3,5,6,7,8,8a-octahydronaphthalene) via an x-ray crystal structure determination on the ethylene thioketal derivative [Kitchens et al. J. Org. Chem. 37, 6 (1972)].
The overall conversion of cis-thujopsene to isomer G (1) is represented below. ##STR1## As readily apparent from the above, the conversion of cis-thujopsene to isomer G (1) involves complex rearrangements of the carbon skeleton which are explained in the reference. The only known methods of producing isomer G, (1), are those described in these references and all involve hydrocarbons derived from naturally occurring oils. Prior to this invention, there was no known way to synthesize the desired 4-acetyl-1,7,7-trimethyltricyclo[6.2.2.0.sup.3,8 ]-3-dodecene (isomer G) without relying on the naturally occurring oil.
It is also evident from a consideration of the known prior art that the isomer G, (1), is only one of a number of compounds produced from the acetylation of thujopsene and must be separated from these other compounds via sophisticated separation techniques before it can be provided in essentially pure form (i.e. &gt;95% pure)